1. Technical Field
The present invention relates to fluid ejection devices and medical devices using the fluid ejection device.
2. Related Art
In the past, a fluid ejection device that converts fluid into a high-pressure pulsating current by varying the volume of a pressure chamber with a volume varying unit formed of a diaphragm and a piezoelectric element and pulsatively ejects the fluid at high velocity out of a nozzle by propagating a pressure wave through a delivery channel pipe from the pressure chamber has been proposed (see, for example, JP-A-2008-82202 (Patent Document 1)).
Moreover, a nozzleless inkjet fluid ejection device that ejects ink by forming, in the bottom of an ink chamber filled with ink, a paraboloidal reflecting plate from which acoustic energy is reflected, exciting a piezoelectric element provided on the ink surface, reflecting acoustic energy by the reflecting plate, and exciting the ink surface by concentrating the acoustic energy onto the focus of the paraboloid has been proposed (see, for example, JP-A-2-95857 (Patent Document 2)).
In the fluid ejection device structured as in Patent Document 1, a plane pressure wave generated in the pressure chamber by the driving of the piezoelectric element propagates through the pressure chamber and the delivery channel pipe communicating with the pressure chamber, the delivery channel pipe having a channel whose diameter is smaller than that of the pressure chamber. At this time, most of the plane pressure wave is reflected off an inner wall that surrounds the delivery channel pipe, the inner wall facing the piezoelectric element. Therefore, it is impossible to transfer the energy of the plane pressure wave to the inside of the delivery channel pipe efficiently.
On the other hand, it was believed that, in the structure as described in Patent Document 2, since the acoustic energy (incidentally, the acoustic energy can be replaced with the energy of the pressure wave) generated by the piezoelectric actuator was reflected from the reflecting plate and was converged onto the focus of the paraboloid located near the surface of the ink, the energy of the pressure wave could be concentrated onto the ink surface efficiently. However, since the acoustic energy which has been made to converge on the focus passes through the focus and then spreads radially because the focus of the paraboloid is provided in an ink ejection port, the ejected ink droplet sometimes breaks up, making it impossible to use the acoustic energy efficiently for ejecting the ink.